A nonaqueous electrolyte solution lithium ion or lithium secondary battery using a carbon material or a lithium metal for a negative electrode and using a lithium-containing composite oxide for a positive electrode is given attention as an electric power supply for cellular phones, notebook computers and the like because a high energy density can be achieved. It is known that a film called a surface film, protective film, SEI or film is generally generated on the surface of the electrode in the secondary battery. It is known that control of the surface film is essential for improvement of the electrode because the surface film has significant influences on the charge and discharge efficiency, the cycle life and the safety. Namely, when a carbon material is used as a negative electrode material, it is necessary to reduce its irreversible capacity, and in the lithium metal negative electrode, it is necessary to solve the problem of reduction in charge and discharge efficiency and the problem as to safety due to generation of dendrite.
As methods for solving these problems, various methods have been proposed. For example, if a lithium metal is used as a negative electrode material, inhibiting generation of dendrite by providing a film layer made of lithium fluoride or the like on the surface of the negative electrode using a chemical reaction has been proposed.
Japanese Patent Laid-Open No. 7-302617 discloses a technique in which a lithium negative electrode is exposed to an electrolyte solution containing hydrofluoric acid and the negative electrode is made to react with hydrofluoric acid to cover its surface with lithium fluoride film. Hydrofluoric acid is generated by a reaction of LiPF6 and a very small amount of water. On the other hand, on the surface of the lithium negative electrode, surface films of lithium hydroxide and lithium oxide are formed by natural oxidization in air. They react, whereby the surface film of lithium fluoride is generated on the surface of the negative electrode. However, this lithium fluoride film is formed using the reaction between an electrode interface and a liquid, side reaction components tend to be included in the surface film, and therefore there are cases where a uniform film cannot be obtained. Furthermore, there are cases where the surface films of lithium hydroxide and lithium oxide are not formed uniformly and an area on which lithium is partially exposed exists, and in these cases, a uniform thin film cannot be formed, and in addition, a problem as to safety due to a reaction between water, hydrogen fluoride, or the like and lithium arises. If the reaction is insufficient, unnecessary compound components other than fluorides may remain, causing adverse effects such as a reduction in ion conductivity. In such a method of forming a fluoride layer using a chemical reaction at an interface, there are cases where the range of choices of available fluorides and electrolyte solutions is limited and it is difficult to form a stable surface film in a high yield.
In Japanese Patent Laid-Open No. 8-250108, a mixed gas of argon and hydrogen fluoride is made to react with an aluminum-lithium alloy to obtain a surface film of lithium fluoride on the surface of a negative electrode. However, if a surface film already exists on the surface of a lithium metal, particularly a plurality of kinds of compounds exist, there are cases where the reaction tends to be uneven so that it is difficult to uniformly form a film of lithium fluoride. In this case, it is difficult to obtain a lithium secondary battery having sufficient cycle characteristics.
Japanese Patent Laid Open No. 11-288706 discloses a technique in which a surface film structure comprising a material having a rock salt crystalline structure as a main component is formed on the surface of a lithium sheet with a uniform crystalline structure, namely a (100) crystalline plane oriented preferentially. It is described that by doing so, a uniform deposition and dissolution reaction, namely charge and discharge of a battery, can be carried out, and dendrite deposition of a lithium metal can be inhibited to improve the cycle life of the battery. It is described that a material that is used for the surface film preferably has a halide of lithium, and a solid solution of at least one selected from a group consisting of LiCl, LiBr and LiI and LiF is used. Specifically, for forming a solid solution film of at least one selected from a group consisting of LiCl, LiBr and LiI and LiF, a lithium sheet fabricated by press processing (rolling) and having a (100) crystalline plane oriented preferentially is immersed in an electrolyte solution containing at least one selected from a group consisting of (1) chlorine molecules or chlorine ions, (2) bromine molecules or bromide ions and (3) iodine molecules or iodine ions, and fluorine molecules or fluorine ions, whereby a negative electrode for a nonaqueous electrolyte battery is fabricated. In this technique, a lithium metal sheet made by rolling is used, the lithium sheet is thus tends to be exposed in air so that films originating from water and the like tend to be formed on the surface, active points unevenly exist, and therefore there are cases where it is difficult to make a desired stable surface film, and in this case the effect of inhibiting dendrite is not necessarily sufficiently obtained.
It is reported techniques relating to improvements of the capacity and charge and discharge efficiency when using a carbon material such as graphite or hard carbon capable of occluding and releasing lithium ions as a negative electrode.
In Japanese Patent Laid-Open No. 5-234583, a negative electrode having a carbon material covered with aluminum is proposed. It is described that reduction decomposition of solvent molecules solvating with lithium ions on the carbon surface is thus inhibited to suppress a degradation in cycle life. However, there are cases where the capacity rapidly decreases when the cycle is repeated because aluminum reacts with a very small amount of water.
In Japanese Patent Laid-Open No. 5-275077, a negative electrode with the surface of a carbon material covered with a thin film of a lithium ion conductive solid electrolyte is presented. It is described that decomposition of a solvent occurring when using a carbon material is thus inhibited, and particularly, a lithium ion secondary battery using propylene carbonate can be provided. However, there are cases where cracks occurring in a solid electrolyte due to a change in stress during insertion and detachment of lithium ions lead to a degradation in characteristics. In addition, there are cases where due to unevenness such as crystal defects of the solid electrolyte, an even reaction is not obtained on the surface of the negative electrode, so that the cycle life is degraded.
Japanese Patent Laid-Open No. 2000-3724 discloses a secondary battery in which the negative electrode is composed of a material containing graphite, a cyclic carbonate and a chain carbonate are used as a main component for the electrolyte solution, and the aforementioned electrolyte solution contains 1,3-propane sultone and/or 1,4-butane sultone as a cyclic monosulfonate in an amount of 0.1 to 4% by weight. Here, 1,3-propane sultone and 1,4-butane sultone are considered to have an effect of contributing to formation of a passivation film on the surface of a carbon material, covering the carbon material highly crystallized by activities of natural graphite and artificial graphite with the passivation film, and inhibiting decomposition of the electrolyte solution without impairing a normal reaction of the battery. In Japanese Patent Laid-Open No. 2000-133304 and U.S. Pat. No. 6,436,582, it is reported that aside from the cyclic monosulfonate, a similar effect is obtained by use of a chain disulfonate. However, in the cyclic monosulfonate of Japanese Patent Laid-Open No. 2000-3724 or the chain disulfonate in Japanese Patent Laid-Open No. 2000-133304 and U.S. Pat. No. 6,436,582, there are cases where formation of a film on a negative electrode first occurs and it is difficult to form a film on, for example, a positive electrode. A method for producing a chain disulfonic acid is disclosed in J. Am. Pham. Assoc., vol. 126, pages 485-493 (1937), G. Schroeter, Lieb, Ann, Der Chemie, vol. 418, pages 161-257 (1919), Biol. Aktiv. Soedin., pp 64-69 (1968) and Armyanskii Khimicheskii Zhurnal, 21, pp 393-396 (1968), and a method for producing a cyclic sulfonate having two sulfonyl groups is disclosed in Japanese Patent Publication No. 5-44946 and U.S. Pat. No. 4,950,768.
In Japanese Patent Laid-Open No. 2003-7334, oxidation of an electrolyte solution solvent is prevented by adding an aromatic compound to the electrolyte solution solvent to inhibit degradation in capacity when repeating charge and discharge of a secondary battery over a long time period. This is a technique for preventing decomposition of a solvent by preferentially oxidizing and decomposing the aforementioned aromatic compound. However, there are cases where when this additive used, the effect of improving the cyclic characteristic cannot be sufficient because the surface of the positive electrode is not covered.
Japanese Patent Laid-Open No. 2003-115324 describes a technique in which the cycle characteristic is improved by adding a nitrogen-containing unsaturated cyclic compound in an electrolyte solution when using a high-voltage positive electrode. However, the nitrogen-containing unsaturated cyclic compound improves the charge and discharge efficiency of the negative electrode, but does not improve the charge and discharge efficiency of the positive electrode.
A lithium-manganese composite oxide having a spinel structure as described in Japanese Patent No. 2996234, Japanese Patent No. 3024636 and Japanese Patent No. 3120789 has been developed as a material that is advantageous for a high-capacity secondary battery because of the high electric potential and inexpensiveness. However, this material is known to cause degradation in capacity resulting from elution of manganese, and various studies have been conducted. For example, Japanese Patent No. 2996234, Japanese Patent No. 3024636 and Japanese Patent No. 3120789 disclose a technique in which hydrogen ions that can be considered to be one of causes of elution of manganese are trapped by a lithium-nickel composite oxide mixed in the positive electrode to inhibit elution of manganese.